Clicking a Button in Another Application

This article provides a simple sample of an application that clicks a button in
another application. The technique could be used for other controls too. For the
purpose of a simple sample the program is a console program. The sample will
click the "=" button in the Windows Calculator Acesssory.

Note that I am using Windows 7; if the Windows Calculator Acesssory in Windows 8
is different and/or cannot be used in the manner it is used here then I hope you
can find another program to use.

The first thing to do is to determine what button to click and the circumstances
of when to click it. Execute the Windows Calculator Acesssory. Type "2+2=" into
it. The result should be 4 of course. Then click the "=" button. Each time "="
is clicked, the value will be increased by 2. So that is something very simple
to automate. We can "manually" execute Calculator and type "2+2=" into it. Then
when we execute our sample application it can just click the "=" button and we
can see the result.

The next thing to do is to determine the identity of the button to be clicked so
our program can click it. With the Windows Calculator Acesssory executing, go to
Visual Studio. In the "Tools" menu is "Spy++". If your system is a 64-bit system
then you might need to use the 64-bit version of Spy++. The Spy++ toolbar will look
like:

Click on the "Find Window" icon; it is a binoculars with a window in the
top-left; it looks like:

That will open a "Find Window" dialog. Now first, ensure that Calculator is
visible; at least the "=" button part of it. Then click on the "Finder Tool"
icon (the square with a circle in it that looks like a target). The "Find Window" dialog looks like:

With the mouse button down, drag from the Finder Tool icon to the "=" button and
release the mouse. The Find Window dialog will be filled in with the "=" button's
handle and other data. Click on "OK". You will then get a "Window Properties"
window with a tab control with five tabs. The five tabs are General, Styles,
Windows, Class and Process. The wndow will look like:

Look for "Contol ID" near the botom of the first (General) tab. It will probably
have the value "00000079". It is a hexadecimal value. Whatever the value is, it
will probably be that value every time you execute that program. At the Windows
API level, controls are often identified by a control id. We can use the Contol
ID shown in the Window Properties window in our program.

We are ready to write the application. I assume you can create a console
application. If your system is 64-bit then you will need to change the "Platform
Target" to "x64". The .Net Process class cannot do everything we need it to do
when our application is not the same as the other application in terms of bits
(32-bits and 64-bits). The "Platform Target" property is in the Build tab of the
project's properties. If you need to automate a 32-bit application from a
64-bit application or 64-bit from 32-bit then you can do that but you will need
to use the Windows API directly to do the equivalent of what we are using the
.Net Process class to do.

You need to add a "using" for the "System.Diagnostics" and
"System.Runtime.InteropServices" namespaces. You will also need to add the
following to the "Program" class:

When we find a process that is executed from there, we know for sure it is the
one we are looking for. Note that there are very many processes in a system;
many more than most people are aware of. Each Windows Service is a process.
Windows Services and other processes that we need to ignore do not have a
window, so we can ignore all processes without a window. The following code will
do all that:

We are ready to click the button from within our application. To click the button we
will send a BN_CLICKED notification message to the button's parent,
the Calculator main window. To do that we will need both the
button id (as in the preceding) and the handle of the button. The handle varies
for each execution but we can determine the handle based on the handle of its
parent and the control id. The Windows API function GetDlgItem does that, as in:

IntPtr hWndButton = GetDlgItem(handle, ButtonId);

Windows messages are sent to a window as determined by the window handle.
Messages also have a message id that specifies what the message is for. We will
send a WM_COMMAND message. The other two parameters we need to send the message
is a wParam and a lParam. The value of those depend on what the message is (the
message id). For a WM_COMMAND message doing what we are doing, the control id is
passed as the high word of wParam and the low word of wParam is the notification
code (BN_CLICKED). The lParam is the handle of the control. It seems unnecessary
to pass both the control id and the control window's handle but that is the way
it works. The following sends the message: